This research is concerned with the perception and processing by normal humans of visual stimulus structure. Stimulus structure involves relations between attributes of stimuli, and total configurations of stimuli. Four major areas of research are: (1) The processing of configural goodness of patterns; (2) The perceived relation between visual letters and the relation of these to ease of processing individual letters; (3) Perception of word configuration under different conditions of stimulus degradation; and (4) The use of hierarchical and contingent information processing strategies. Methods used include classification, identification, stimulus comparison, and stimulus discrimination, with both errors and reaction times as the common form of performance measure.